This is a K08 award application for Dr. Jennifer Nayak, a Pediatric Infectious Diseases subspecialist at the University of Rochester. Dr. Nayak is a young investigator establishing herself in the field of influenza immunology. The period of support offered by this K08 award will provide Dr. Nayak with the time and mentorship needed to acquire the knowledge, technical skills, and critical thought processes necessary in a successful independent researcher. During this time period, she will become adept at utilizing biostatistics to more effectively design experiments and analyze results, expand her skills in a broad range of experimental techniques, gain experience mentoring junior fellows and students engaged in similar areas of research, and increase her collaborations with faculty both within and outside of the University of Rochester. To achieve these goals, Dr. Nayak's primary mentor will be Dr. Andrea Sant, an established researcher with expertise in CD4 T cell biology and the CD4 T cell response to influenza. The proposed research addresses the fact that current pandemic influenza vaccination strategies are inadequate because the inability to predict the next pandemic strain and the time required for vaccine production lead to inadequate global protection in the face of a spreading pandemic. The objective is to understand how CD4 T cell specificity affects B cell and antibody responses on secondary infection or vaccination with a novel influenza strain, with the long-term goal of enhancing the potential of an individual to respond to novel influenza strains through optimal vaccination strategies that increase neutralizing antibody production. Based on preliminary data demonstrating decreased HA-specific CD4 T cells and antibody following a heterosubtypic influenza infection with a virus containing both novel and conserved epitopes, the central hypothesis that prior selective expansion of HA-specific CD4 T cells will result in more robust neutralizing antibody production in the setting of heterosubtypic infection or pandemic vaccination was developed. This hypothesis will be tested by 1) determining if selective expansion of HA-specific CD4 T cells facilitates B cell reactivity to novel epitopes and enhances HA-specific antibody production on heterosubtypic infection; and 2) evaluating if initial vaccination with a recombinant avian protein in the setting of prior immunity to seasonal influenza enhances HA-specific CD4 T cell and antibody responses on boosting with an inactivated avian vaccine. The proposed research will fill a critical gap in the understanding of the role of HA-specific CD4 T cells in both heterosubtypic infection and vaccination, potentially providing the first step towards a viable pre pandemic vaccination strategy that selectively arms the CD4 T cell compartment. This innovative approach to pandemic vaccination could promote accelerated neutralizing antibody production following natural infection or immunization with a novel influenza strain, enhancing individual pandemic protection, improving post-pandemic vaccine efficacy, and ultimately mitigating the impact of the next influenza pandemic.